According to the difference of CRHOL under VTD and
VMD electrode, it is inferred that this difference related to the
discharge initiation position (as Figure 16). During positive
half-cycle of applied voltage, the discharge initiation position
located in the vicinity of interface between gas and PE in the
usage of VMD electrode. Although the decay of positive
surface charges was significant when voltage cycle increased,
residual positive charges nearby the interface could inhibit the
production of seed electrons that could initiate new homodischarges.
Therefore, the subsequent ones tended to take
place at the sites without positive surface charges. During
negative half-cycle of applied voltage, the discharge initiation
position located in the vicinity of high-voltage electrode. The
free electrons resulting from secondary electron emission
caused by the impact of positive charges on the cathode could
trigger new discharge, and the discharge location may
coincide with the charge spot generated by the former
negative discharges. However, when voltage cycle was small
(e.g. 20 ms) the surface charges generated by discharges in a
half-cycle could reduce the applied field, causing the result
that discharge did not occur at the sites with homo-charges.
As voltage cycle increased, due to the charge decay, the
reduction of local field was decreased, so CRHOL became
larger. With VTD electrode, discharge always started at the
interface with positive surface charges. Therefore, there was
no coincidence of homo-discharges in a half-cycle.